Ultrasonic cardiac output monitor

ABSTRACT

A method of cardiac physiologic monitoring is disclosed comprising the steps of: (a) utilizing an external ultrasonic transducer element attached to a patient to determine an information signal indicating of blood floe within a patient&#39;s heart; (b) processing the information signal to determine physiologic parameters associated with the heart. The physiologic parameters can include at least one of transaortic peak velocity, mean transvalvular pressure gradient, time velocity integral, stroke volume, cardiac output or any other product as an analogue of output. The method can preferably include monitoring the change in time of the physiologic parameters through continual monitoring of the information signal. The monitoring step preferably can include determining an alarm state if the parameters are preferably outside a predetermined range. The external ultrasonic transducer preferably can include an attached handle operative to position the transducer in a predetermined orientation to the patient&#39;s heart.

FIELD OF THE INVENTION

The present invention relates to the field of cardiac monitoring and, inparticular, discloses a method for utilisation of an external transducerelement in ultrasonic cardiac monitoring.

BACKGROUND OF THE INVENTION

The process of accurate cardiac physiologic monitoring is obviously animportant process during acute illness and anaesthesia. In particular,early detection of changes in cardiac function can be critical in thereduction of patient morbidity and mortality.

Current methods of direct cardiac monitoring are expensive, technicallydifficult to operate and provide for variable results.

One common form of monitoring is the electrocardiographic method whichmonitors the electrical cardiac activity. Unfortunately, this methodonly provides for an indirect monitoring of cardiac muscle conductivityand not blood flow. Also currently utilised is an ultrasonic method ofcardiac physiologic monitoring utilising 2D transoesophagealechocardiographic ventricular transections. However, this method isinvasive, expensive and inaccurate by virtue of its technical difficultyand that only 6 of 16 myocardial segments are imaged at any time.Unfortunately, normal left ventricular myocardial function variestransmurally, transtemporally and intersegmentally and the 2D evaluationof the wall motion requires spatial and temporal integration skills onlyacquired after a programme of extensive and expensive physiciantraining.

There is therefore a general need for an improved, more convenient formof cardiac physiologic monitoring.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide for an improved formof cardiac physiologic monitoring utilising ultrasound techniques.

In accordance with a first aspect of the present invention, there isprovided a method of cardiac physiologic monitoring comprising the stepsof:

(a) utilising an external ultrasonic transducer element attached to apatient to determine an information signal indicative of blood flowwithin a patient's heart;

(b) processing the information signal to determine physiologicparameters associated with the heart function.

The physiologic parameters can include at least one of transaortic peakvelocity, mean transvalvular pressure gradient, time velocity integral,stroke volume, cardiac output or any other product as an analogue ofoutput.

The method can preferably include monitoring the change in time of thephysiologic parameters through continual monitoring of the informationsignal.

The monitoring step preferably can include determining an alarm state ifthe parameters are outside a predetermined range.

The external ultrasonic transducer preferably can include an attachedhandle operative to position the transducer in a predeterminedorientation to the patient's heart.

In accordance with a further aspect of the present invention, there isprovided a cardiac monitoring system comprising: an external ultrasonictransducer element adapted to be attached to a patient to provide aninformation signal indicative of blood flow within a patient's heart;computer processing means, interconnected to the transducer element andadapted to process the information signal to determine physiologicparameters associated with the heart.

The physiologic parameters can include at least one of transaortic peakvelocity, mean transvalvular pressure gradient, time velocity integral,stroke volume, cardiac output or any other product as an analogue offlow.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms which may fall within the scope of thepresent invention, preferred forms of the invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings in which:

FIG. 1 illustrates an example output of a ventricular insonation;

FIGS. 2 and 3 illustrate various features of the output of FIG. 1;

FIG. 4 is a perspective view of an arrangement of the preferredembodiment when utilised to monitor a patient;

FIG. 5 illustrates a sectional view of the transducer element;

FIG. 6 is a functional block diagram of the preferred embodiment; and

FIG. 7 illustrates an example form of user interface suitable for usewith the preferred embodiment.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

In the preferred embodiment simple Doppler echocardiographic evaluationof cardiac blood flow is utilised to provide accurate and reproduciblecardiac output information which allows for the utilization of equipmentthat is simple in design, durable, inexpensive to manufacture and easyto operate.

In the preferred embodiment, transaortic and transpulmonary continuouswave (CW) Doppler analysis is adapted for use as a heart monitoringdevice. Continuous wave Doppler is well validated and a routineechocardiographic method of quantitating cardiac output with low interand intra observer variability.

Turning to FIG. 1, there is illustrated an example CW screen grab output1 from a 7777 device which provides for a measure of blood velocity overtime. The CW method detects the velocity of individual blood cells bymeasuring the frequency change of a reflected ultrasound beam anddisplaying this as a time velocity flow profile as indicated in FIG. 1.

Appropriately directed Doppler insonation from the apical orsuprasternal acoustic window provides a time velocity profile oftransaortic flow, while insonation from the parasternal window providesa transpulmonary flow profile. This flow profile is an analogue ofcardiac output and is a real time stroke to stroke measure of cardiacphysiology.

The preferred embodiment utilizes the flow profile to generate acorresponding change monitoring of the flow profile with time. Thespectral flow profile can be image processed to be accurately edgedetected, providing a real time computed read out of transaortic peakvelocity (Vpk) Heart Rate (HR), means transvalvuar pressure gradient(Pmn), tire velocity integral (tvi) and, with a premeasured acrtic (Ao)or pulmonary artery (PA) diameter from a 2D examination, cardiac output(CO) or any other product as an analogue of output can be determined.The measures (Vpk), tvi and HR are illustrated in FIG. 2.

Intracardiac flow across the aortic valve and the pulmonary valve mustbe equal in the absence of significant regurgitation or trans-septalflow (shunt), and regardless, both can be used to reflect changes incardiac output, so the choice of whether transpulmonary or transaorticmonitoring is chosen can depend only on the ease of signal access.

Although absolute flow can be determined using aortic valve or pulmonaryartery diameter derived from a 2D echocardiogram, this may not berequired as the relevance of physiologic monitoring is dependent ondetecting temporal changes in output. Therefore, a change from eitherthe baseline transoartic or transpulmonary profile would, providingthere was no significant change in the angle of insonation, represent achange in output proportional to the change in the baseline parameters(tvi, Pmn, Vpk and CO) etc.

In the preferred embodiment normal variance ranges for haemodynamicparameters can be preferably user selected from the reference cycles sothat an alarm would sound if signals exceeded this range. As illustratedin FIG. 3, the tolerance for alarm activation for (Vpk) could be astepped user selected variable set to compensate for individual baselinestroke to stroke variability (−15%, −20%, −30% etc).

Arrhythmias are associated with cardiac disease and can produce highstroke to stroke variability of haemodynamic parameters making automatedsingle cycle signal analysis unrepresentative. This can be addressedusing multi cycle signal averaging so that a user selected variablenumber of cycles would be averaged to give mean Vpk, Pmn, tvi and COparameters for alarm detection and the setting of wide alarm parametersfor stroke to stroke variability.

The direct measurement of transpulmonary flow can be achieved byapplying a small CW transducer with an adherent gel coupling layer tothe surface of the skin at the left parasternal acoustic window;adjacent to the sternum in an intercostal interspace, while thetransaortic flow can be detected from the intercostal space associatedwith the palpable ventricular apex beat or from the suprasternal notch.The transducer can be fixed in place with adhesive tape or sheet and ora transthoracic belt utilising a thin gel coupling layer to ensuretransducer skin contact.

In FIG. 4 there is illustrated an example arrangement with a patient 10being monitored utilising a transducer element 11 interconnected with acomputer signal processing unit 12.

In FIG. 5, there is illustrated an enlarged sectional view of thetransducer element 11 which includes a transducer 15 attached to apositioning device 16 which can be utilised to initially set theposition of the transducer. Between the transducer 15 and a person'sskin 17 is placed a gel coupling layer 18 for coupling the ultrasonictransducer vibrations to the skin 17.

Turning now to FIG. 6, there is illustrated, in functional block diagramform, one form of construction of the computer system 12 of FIG. 4. Thesystem 12 includes a master oscillator 20 which is interconnected to atransmitter 21 which is responsible for transmitting the oscillation totransducer 11. The transducer 11 includes receiver 22 which is forwardedto a demodulating element 23 which utilises phase outputs from themaster oscillator 20 so as to demodulate the received signal fromreceiver 22 so as to provide for a spectral output which is forwarded toa spectral analyser 24 which can in turn include a computer digitalsignal processor arrangement for processing the output signal so as todetermine the relevant parameters. The spectral analyser 24 can comprisea computer type device with appropriate DSP hardware. The spectralanalyser 24 outputs to a spectral display 25 which can include astandard user interface of relevant information. For example, in FIG. 7,there is shown an example display output which includes buttons forsetting various sensitivity and alarm ranges so as to provide for fullcardiac physiologic monitoring.

The continuous wave ultrasound transducer (1.0 to 3.0 Mhz) 11 caninclude a small raised toggle for angular adjustment. The transducer canbe strapped to the left ventricular apical intercostal window, the leftparasternal intercostal window or the suprasternal notch and fixed inplace wrath an adhesive sheet or tape, and a belt.

Turning now to FIG. 7, there is illustrated the steps involved in themethod of requisite features extraction by the DSP processor. The steps30 rely on standard image processing techniques well known to thoseskilled in the art of computer image processing.

Initially, a first CW image is captured 31. From this image, the edgesare extracted 32 and analyzed so as to determine the relevant perameters33, By repeating the process 31-33 for multiple frames, it is possibleto determine variations in time base perameters 34. These variations canbe saved 35 or output 36 for display and monitoring.

Obviously, many different arrangements of a system are possible. Thesystem could be utilised as a stand alone physiologic monitor,integrated with oximetry, ECG etc or to provide for a remote monitorwith on-board analysis or remote transmission.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects to be illustrative andnot restrictive.

What is claimed is:
 1. A method of cardiac physiological monitoring of apatient, comprising the steps of: (a) utilizing a transcutaneousultrasonic transducer element attached to the patient to monitordirectly the transvalvular cardiac flow of fluid through the cardiacvalves of the patient's heart and to generate an information signalindicative of fluid flow within the patient's heart; (b) processing saidinformation signal to determine one or more physiological parametersassociated with the heart.
 2. A method as claimed in claim 1 externalultrasonic transducer element monitors the flow within the heart fromthe patient's chest using the parasternal or apical thoracic acousticaccess.
 3. A method as claimed in claim 1 wherein said physiologicalparameters include as least one of transaortic peak velocity, meantransvalvular pressure gradient, time velocity integral, stroke volumeor cardiac output.
 4. A method as claimed in claim 1 further comprisingthe step: (c) monitoring the change with time of said physiologicalparameters through continual monitoring of said information signal.
 5. Amethod as claimed in claim 1 wherein said monitoring step includesdetermining an alarm state if said parameters are outside apredetermined range.
 6. A method as claimed in claim 1 wherein saidexternal ultrasonic transducer includes an attached handle operative toposition said transducer in a predetermined orientation to saidpatient's heart.
 7. The method of claim 1 wherein the fluid is blood. 8.A cardiac monitoring system for use with a patient, comprising: atranscutaneous ultrasonic transducer element adapted to be attached tothe patient and to monitor directly the transvalvular cardiac flow offluid flowing through cardiac valves of the patient's heart and tothereby provide an information signal indicative of fluid flow withinthe patient's heart, computer processing means interconnected to saidtransducer element and adapted to process said information signal todetermine one or more physiological parameters associated with theheart.
 9. A cardiac monitoring system as claimed in claim 8 wherein saidexternal ultrasonic transducer element is adjusted to be affixed to aparasternal or apical thoracic acoustic access point.
 10. A cardiacmonitoring system as claimed in claim 8 wherein said physiologicalparameters include at least one of transaortic peak velocity, meantransvalvular pressure gradient, time velocity integral, stroke volumeor cardiac output.
 11. A cardiac monitoring system as claimed in claim 8further comprising: alarm means interconnected to said computerprocessing means and adapted to emit an alarm if said parameters areoutside a predetermined range.
 12. A cardiac monitoring system asclaimed in claim 8 wherein said external ultrasonic transducer elementincludes an attached handle operative to position said transducer in apredetermined orientation to said patient's heart.
 13. The system ofclaim 8 wherein the fluid is blood.